The present invention relates to a retractor (a winding device) for use with a seat belt webbing device and, in particular, to a retractor for use with a seat belt webbing which includes an energy absorbing mechanism using a torsion bar.
Conventionally, as a retractor for use with a seat belt webbing which is used to hold an occupant or the like of an vehicle in a seat safely, there are used many kinds of retractors of an emergency lock type which includes an emergency lock mechanism for locking a retractor physically by means of inertia sensing means capable of responding to sudden acceleration, vehicle collision or sudden deceleration, whereby the vehicle occupant can be restricted effectively and safely.
As a retractor of this emergency lock type, there is known a structure that a cylindrical-shaped bobbin around which a webbing can be wound is formed integrally of light material such as synthetic resin, a light alloy or the like, and a winding shaft serving as a strength member formed of steel material by forging is fitted or inserted into the bobbin and is then rotatably supported on a retractor base, thereby forming a light and high-strength winding shaft assembly.
And, the winding shaft includes lock means structured such that a locking base provided in one end portion thereof can be engaged with the engaging portion of the retractor base in a vehicle emergency to thereby prevent the winding shaft from rotating in the webbing pull-out direction thereof; that is, the winding shaft is structured such that, in a vehicle emergency, the locking base thereof can be engaged with the engaging portion of the retractor base to thereby prevent the winding shaft assembly against rotation in the webbing pull-out direction thereof.
By the way, in a retractor of an emergency lock type structured in the above-mentioned manner, as a fixing structure which is used to fix the base end portion of the webbing to the winding shaft assembly, there is known a fixing structure which is disclosed in Japanese Utility Model Unexamined Publication No. Sho. 60-87749 and the like.
In particular, as shown in FIG. 1, a winding shaft assembly 100 includes a bobbin 102 which is formed of light material in an integrally cylindrical shape and around the outer periphery of which a webbing 101 can be wound, and a winding shaft 103 which is formed of steel material and serves as a strength member assembled to the center hole of the bobbin 102. Also, the bobbin 102 and winding shaft 103 respectively include slits 121 and 122 which respectively extend through the bobbin 102 and winding shaft 103 in the diameter directions thereof, so that the base end portion of the webbing 101 can be inserted through the slits 121 and 122.
And, the base end portion of the webbing 101 is inserted from one opening end 121a of the slit 121, is passed through the slit 122, is further passed through the slit 121, and is projected from the other opening end 121b thereof; and, at the same time, a substantially rod-shaped fixing pin 130 having an outside diameter larger than the gap of the two slits is inserted into a loop-shaped portion 110 formed by turning back and sewing the base end portion of the webbing 101 to thereby form a large diameter portion 120, so that the base end portion of the webbing 101 is prevented against the removal from the winding shaft 103. That is, the webbing 101 can be secured to the winding shaft assembly 100.
The above-mentioned fixing structure not only is easy to secure a sufficient fixing strength but also is so simple in structure that it can be assembled easily and efficiently.
On the other hand, in a retractor of an emergency type, when the emergency lock mechanism is operated due to a collision to prevent the webbing from being pulled out, if the shock due to the collision is very heavy, with the passage of time after the collision, a tensile force acting on the webbing increases to thereby cause a sudden deceleration in the body of the vehicle occupant, so that a load given to the occupant from the webbing becomes extremely large. In view of this, recently, there have been proposed various kinds of retractors for use with a seat belt webbing; in particular, each of them includes an energy absorbing mechanism which, when the tensile force acting on the webbing reaches or exceeds a previously set given value, pulls out the webbing a given amount to thereby absorb the shock produced in the body of the occupant, so that the body of the occupant can be protected more positively.
And, as the retractor for use with a seat belt webbing including the above-mentioned energy absorbing mechanism, there are proposed various retractors (see Japanese Patent Unexamined Publications Nos. Hei. 6-156884, Hei. 7-47923, and the like; each of them comprises a substantially cylindrical shaft assembly around which a webbing can be wound, a torsion bar which can be inserted through the center hole of the winding shaft assembly in such a manner that one end thereof is connected to the winding shaft assembly in a mutually unrotatable manner and the other end thereof is connected to the locking base of the winding shaft assembly in a mutually unrotatable manner, and emergency lock means which, in a vehicle emergency, engages the locking base with the retractor base of the retractor to prevent the rotation of the torsion bar to thereby prevent the winding shaft assembly against rotation in the webbing pull-out direction thereof, whereby, when the emergency lock means is put into operation, if a tensile force acting on the webbing exceeds a previously set given value, then not only the shock energy can be absorbed by means of the torsional deformation of the torsion bar but also the tensile force acting on the webbing can be controlled.
As described above, the structure for absorbing the collision energy by means of the torsional deformation of the torsion bar inserted through the center hole of the winding shaft assembly not only is higher in the freedom of design with respect to the energy absorbing amount and the pull-out amount of the webbing, but also is simpler in structure and is thus more suitable for the reduction of the size of a retractor, when compared with a structure for absorbing the collision energy by means of the plastic deformation of the winding shaft assembly itself, retractor base or the like.
However, in such a webbing fixing structure as shown in FIG. 1, when trying to insert the above-mentioned torsion bar into the center hole of the winding shaft assembly, the torsion bar cannot be inserted because the webbing is in the way. Therefore, for example, as disclosed in the above-cited Japanese Patent Unexamined Publication No. Hei. 6-156884 and the like, there is employed a structure in which the torsion bar is inserted into the cylindrical portion formed by turning back and sewing the base end portion of the webbing to prevent the webbing against removal, thereby being able to secure the base end portion of the webbing to the winding shaft assembly.
However, as a result of this, after the cylindrical portion of the webbing is disposed within an inwardly spreading opening formed in the winding shaft assembly, the torsion bar must be inserted into the present cylindrical portion, which lowers the efficiency of the assembling operation of the winding shaft assembly. Also, if the base end portion of the webbing is pulled in the removing direction thereof due to a tensile force acting on the webbing in a vehicle collision, then a bending force and friction resistance are applied to the torsion bar, which has influences on the energy absorbing load to be deal with by means of the torsional deformation of the torsion bar.
In view of the circumstances of the prior art, the present invention aims at eliminating the drawbacks found in the above-mentioned conventional retractors. Accordingly, it is an object of the invention to provide a retractor for use with a seat belt webbing which not only can absorb a collision energy by means of a torsion bar inserted through a center hole formed in a winding shaft assembly but also can secure the base end portion of a webbing simply and firmly to the winding shaft assembly.
In attaining the above object, according to the invention, there is provided a retractor for use with a seat belt webbing, comprising:
a retractor base;
a substantially cylindrical-shaped winding shaft assembly which is integraly formed and is rotatably supported on the retractor base and around which a seat belt webbing can be wound;
a torsion bar to be inserted through a center hole formed in the winding shaft assembly in such a manner that one end thereof is connected to the winding shaft assembly in a mutually unrotatable manner and the other end thereof is connected to a locking member in a mutually unrotatable manner;
an emergency lock mechanism which, in a vehicle emergency, connects the locking member to the retractor base to stop the rotation of the torsion bar to thereby prevent the winding shaft assembly from rotating in the webbing pull-out direction thereof, the emergency lock mechanism being structured such that, when the emergency lock mechanism is in operation and also a tensile force acting on the webbing exceeds a given value, the emergency lock mechanism can absorb a shock produced in the body of an occupant by means of the torsional deformation of the torsion bar;
a slit which is formed in the winding shaft assembly and penetratingly extends in a direction crossing the winding shaft assembly while substantially passing an area located outside ann area interrupting an insertion position of the torsion bar;
a large diameter portion being larger in size than a width of the slit and including an loop-shaped end portion of the webbing; and
a preventive portion, disposed between the large diameter portion and the torsion bar, for preventing the large diameter portion from moving in a direction approaching the torsion bar, wherein the preventive portion comprises a projecting portion disposed on a surface of the slit that is located near to said torsion bar and projected into a space between the torsion bar and the large diameter portion.
According to the above structure, since the base end portion of a webbing is inserted through a slit formed in a winding shaft assembly and, in the base end portion of the webbing that has passed through and projected from the slit, there is formed a large diameter portion larger in size than the gap of the slit to thereby prevent the webbing base end portion against removal, not only the base end portion of the webbing can be secured to the winding shaft assembly simply and firmly but also the large diameter portion is prevented from interfering with or from being strongly pressed against a torsion bar and thus has no influence on the energy absorbing load due to the torsional deformation of the torsion bar.
In addition, with the above structure, it is possible to prevent the torsion bar from being brought in contact with a seat belt webbing which is drawn from the large diameter portion or reduce an excessive bending force which is generated by the seat belt webbing drawn from the large diameter portion and is then applied to the torsion bar. Preferably, in order that the base end portion of the webbing can be made to adjoin the torsion bar, the slit of the winding shaft assembly may be formed in communication with the center hole of the winding shaft assembly; and, at the same time, in order to be able to prevent the large diameter portion from interfering with the torsion bar due to the tensile force acting on the webbing, a portion of the winding shaft assembly, in which the slit is formed, may be projected in such a manner that it can separate the large diameter portion and the torsion bar from each other.
With use of the above-mentioned structure, since the formation position of the slit can be made to approach to one diameter direction of the winding shaft assembly, the strength of the winding shaft assembly can be secured easily.
In the above-mentioned structure, advantageously, the center hole of the winding shaft assembly is communicated with the slit thereof.
Moreover, in the above-mentioned structure, advantageously the large diameter portion is larger in size than the width of the slit, and is also larger in size than the center hole of the winding shaft assembly.
In the above-mentioned retractor according to the present invention, preferably, the end portion of the slit where the large diameter portion is situated is formed in a recessed portion having a shape substantially corresponding to the large diameter portion.
Further, in the above-mentioned retractor according to the present invention, advantageously, the slit is defined by a pair of surfaces, one of which is located near the torsion bar, and the one is disposed at position apart from the torsion bar by a distance which is not less than a radius of the torsion bar.
In addition, the above-object can also be achieved by a retractor for use with a seat belt webbing, according to the other aspect of the present invention, comprising:
a retractor base;
a substantially cylindrical-shaped winding shaft assembly which is rotatably supported on the retractor base and around which a seat belt webbing can be wound;
a torsion bar to be inserted through a center hole formed in the winding shaft assembly in such a manner that one end thereof is connected to the winding shaft assembly in a mutually unrotatable manner and the other end thereof is connected to a locking member in a mutually unrotatable manner;
an emergency lock mechanism which, in a vehicle emergency, connects the locking member to the retractor base to stop the rotation of the torsion bar to thereby prevent the winding shaft assembly from rotating in a webbing pull-out direction thereof, the emergency lock mechanism being structured such that, when the emergency lock mechanism is in operation and also a tensile force acting on the webbing exceeds a given value, the emergency lock mechanism can absorb a shock produced in the body of an occupant by means of the torsional deformation of the torsion bar;
a slit which is formed in the winding shaft assembly and penetratingly extends in a direction crossing the winding shaft assembly while substantially passing an area located outside an area interrupting an insertion position of the torsion bar; and
a large diameter portion being larger in size than a width of the slit and including an loop-shaped end portion of the webbing,
wherein the slit is defined by a pair of surfaces one of which has a portion located near the torsion bar and disposed at a position apart from a line passing through the center of the winding shaft assembly and extending in parallel with an slit extending direction by a distance which is substantially equal to a radius of the torsion bar.
Further, the above-mentioned object can be attained by a retractor for use with a seat belt webbing, according to another aspect of the present invention, comprising:
a retractor base;
a substantially cylindrical-shaped winding shaft assembly which is rotatably supported on the retractor base and around which a seat belt webbing can be wound;
a torsion bar to be inserted through a center hole formed in the winding shaft assembly in such a manner that one end thereof is connected to the winding shaft assembly in a mutually unrotatable manner and the other end thereof is connected to a locking member in a mutually unrotatable manner;
an emergency lock mechanism which, in a vehicle emergency, connects the locking member to the retractor base to stop the rotation of the torsion bar to thereby prevent the winding shaft assembly from rotating in a webbing pull-out direction thereof, the emergency lock mechanism being structured such that, when the emergency lock mechanism is in operation and also a tensile force acting on the webbing exceeds a given value, the emergency lock mechanism can absorb a shock produced in the body of an occupant by means of the torsional deformation of the torsion bar;
a slit which is formed in the winding shaft assembly and penetratingly extends in a direction crossing the winding shaft assembly while substantially passing an area located outside an area interrupting an insertion position of the torsion bar;
a large diameter portion being larger in size than a width of the slit and including an loop-shaped end portion of the webbing; and
a preventive portion, disposed between the large diameter portion and the torsion bar, for preventing the large diameter portion from moving in a direction approaching the torsion bar, wherein the preventive portion comprises a projecting portion, disposed on a surface of the slit that is located near to the torsion bar and projected into a space between the torsion bar and the large diameter portion, to thereby reduce a bending force which is generated by the webbing projected from the large diameter portion and then applied to the torsion bar.
In the above-mentioned construction, it is preferable that the projecting portion is disposed at a position apart from a line passing through the center of the winding shaft assembly and extending in parallel with an slit extending direction by a distance which is substantially equal to a radius of the torsion bar.